There has been a demand for some time for a modern apparatus used to treat and prepare food that can adapt its treatment and preparation methods as much as possible to the food, i.e. that can control the cooking chamber climate as much as possible. Increased moisture in the gas mixture in the cooking chamber is necessary for different treatment and preparation steps or processes, such as “steaming”. While detecting the temperature in the cooking chamber is relatively simple and reliable, the detection of the moisture in the gas mixture in the cooking chamber can be quite difficult.
Complex moisture sensors have previously been proposed, such as the one disclosed in GB 2 207 514 A. Moisture sensors of this kind are not very reliable, their structure is expensive, and they are seriously subject to contamination.
Turning away from the direct moisture measurement, the indirect moisture detection approach was established among the experts, wherein different methods of detection were suggested.
An indirect method of detecting the moisture is known from DE 42 06 845 C2, in which a pressure difference in a flow within the gas mixture is built up by a rotor. This pressure difference is measured and the density of the gas mixture is derived therefrom. The density is used for determining the portion that is water vapor.
The disadvantage of this method is, however, the very low pressure difference of 1 to 2 mbar that results. Consequently, on the one hand, expensive measuring means for determining the small pressure difference are required and, on the other hand, the smallest fluctuations can lead to a result that is not decisive.
The method according to DE 100 02 309 C1 goes in a different direction Here the difference between the rotational speed generated when driving the gas conveyance and circulation means as compared to the synchronous speed of the asynchronous motor, i.e. the slip, is used as a measure of the portion of the gas component sought by taking predetermined pressure and temperature values of the gas mixture into consideration.
Here again, since pressure-dependent values are important, reliable pressure detection remains necessary. Moreover, even though the slip results from the difference between the specific standard speed of the asynchronous motor and the actual speed, other influences on the actual speed, such as the properties of the voltage supply, the degree of wear to the components of the motor as well as of the entire apparatus, etc, are left out of consideration. This affects the preciseness of detection on the one hand, and, on the other hand, requires a very high expenditure on technical apparatus.